For future air conditioning systems installed in motor vehicles, it is to be expected that the usual R134a air conditioners will be replaced by CO2 air conditioners, since, according to EU legislation, the cooling agent R134a, used up until now, will be totally prohibited as of the year 2016.
By contrast to the conventional air conditioner that is operated using cooling agent R134a, in the CO2 air conditioner, both a pressure signal and a temperature signal from the compressor of the air conditioner will be required for the regulation of the air conditioner. The use of two sensors represents a considerable expenditure, since at least two plug connectors and several strands of cable have to be held in reserve, as well as sealing locations that have to be sealed at the interface locations and connecting locations of the individual components among one another. An attempt is made, therefore, to obtain both the pressure signal and the temperature signal by a combination of a pressure sensor and a temperature sensor.
Combined pressure and temperature sensors are known, for instance, from European Published Patent Application No. 1 521 061, German Published Patent Application No. 101 09 095, as well as German Published Patent Application No. 197 45 244, and European Published Patent Application No. 0 863 676. In the design approach according to German Published Patent Application No. 101 09 095, a front diaphragm sensor is used having a mounted plunge sensor. However, this design approach suffers from the disadvantage that the front diaphragm sensor is very sensitive in the vicinity of the diaphragm, and a protective screen should be preconnected. In the case of this design approach, it is used in racing car applications whose service life is extremely short. The design approach according to German Published Patent Application No. 197 45 244 describes a separate threaded part for the temperature sensor, which is sealed using a simple O-ring. However, the O-ring becomes brittle during a longer operating period, so that leakage sets in.
A further design approach possibility known from the related art relates to using the input resistance of a pressure-measuring bridge that is applied to a diaphragm so as to obtain a temperature signal. Based on the circumstance that the diaphragm is located relatively far from the measured medium, the temperature signal received is too inaccurate. However, in order to measure as far as possible in the measured medium, a complex construction technology and connecting technology are used. If the sensor extends into the measuring channel, it narrows down the channel, because of its cross section, to such an extent that considerable pressure reduction can occur, which impairs the measurement of the pressure signal.
The design approaches sketched above, known from the related art, do not represent satisfactory solutions for the reasons mentioned.